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1. Female Pacific walruses (Odobenus rosmarus divergens) show greater partitioning of sea ice organic carbon than males: Evidence from ice algae trophic markers

   https://doi.org/10.1371/journal.pone.0255686  

   Koch, Chelsea W.; Cooper, Lee W.; Woodland, Ryan J.; Grebmeier, Jacqueline M.; Frey, Karen E.; Stimmelmayr, Raphaela; Magen, Cédric; Brown, Thomas A. (August 2021, PLOS ONE)

   Mancinelli, Giorgio (Ed.)

   The expected reduction of ice algae with declining sea ice may prove to be detrimental to the Pacific Arctic ecosystem. Benthic organisms that rely on sea ice organic carbon (iPOC) sustain benthic predators such as the Pacific walrus ( Odobenus rosmarus divergens ). The ability to track the trophic transfer of iPOC is critical to understanding its value in the food web, but prior methods have lacked the required source specificity. We analyzed the H-Print index, based on biomarkers of ice algae versus phytoplankton contributions to organic carbon in marine predators, in Pacific walrus livers collected in 2012, 2014 and 2016 from the Northern Bering Sea (NBS) and Chukchi Sea. We paired these measurements with stable nitrogen isotopes ( δ 15 N) to estimate trophic position. We observed differences in the contribution of iPOC in Pacific walrus diet between regions, sexes, and age classes. Specifically, the contribution of iPOC to the diet of Pacific walruses was higher in the Chukchi Sea (52%) compared to the NBS (30%). This regional difference is consistent with longer annual sea ice persistence in the Chukchi Sea. Within the NBS, the contribution of iPOC to walrus spring diet was higher in females (~45%) compared to males (~30%) for each year (p < 0.001), likely due to specific foraging behavior of females to support energetic demands associated with pregnancy and lactation. Within the Chukchi Sea, the iPOC contribution was similar between males and females, yet higher in juveniles than in adults. Despite differences in the origin of organic carbon fueling the system (sea ice versus pelagic derived carbon), the trophic position of adult female Pacific walruses was similar between the NBS and Chukchi Sea (3.2 and 3.5, respectively), supporting similar diets (i.e. clams). Given the higher quality of organic carbon from ice algae, the retreat of seasonal sea ice in recent decades may create an additional vulnerability for female and juvenile Pacific walruses and should be considered in management of the species. 

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2. Year-round utilization of sea ice-associated carbon in Arctic ecosystems

   https://doi.org/10.1038/s41467-023-37612-8  

   Koch, Chelsea W.; Brown, Thomas A.; Amiraux, Rémi; Ruiz-Gonzalez, Carla; MacCorquodale, Maryam; Yunda-Guarin, Gustavo A.; Kohlbach, Doreen; Loseto, Lisa L.; Rosenberg, Bruno; Hussey, Nigel E.; et al (December 2023, Nature Communications)

   Abstract Sea ice primary production is considered a valuable energy source for Arctic marine food webs, yet the extent remains unclear through existing methods. Here we quantify ice algal carbon signatures using unique lipid biomarkers in over 2300 samples from 155 species including invertebrates, fish, seabirds, and marine mammals collected across the Arctic shelves. Ice algal carbon signatures were present within 96% of the organisms investigated, collected year-round from January to December, suggesting continuous utilization of this resource despite its lower proportion to pelagic production. These results emphasize the importance of benthic retention of ice algal carbon that is available to consumers year-round. Finally, we suggest that shifts in the phenology, distribution and biomass of sea ice primary production anticipated with declining seasonal sea ice will disrupt sympagic-pelagic-benthic coupling and consequently the structure and the functioning of the food web which is critical for Indigenous Peoples, commercial fisheries, and global biodiversity. 

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3. Trends in benthic macrofaunal populations, seasonal sea ice persistence, and bottom water temperatures in the Bering Strait region

   https://doi.org/10.5670/oceanog.2018.224  

   Grebmeier, Jacqueline M.; Frey, Karen E.; Cooper, Lee W.; Kedra, K. (January 2018, Oceanography)

   Recent declines in sea ice extent and warming seawater temperatures in the Arctic have the potential to impact regional and pan-Arctic marine ecosystems. To investigate marine biological response to these key drivers and other environmental factors, we undertook a robust trend analysis of benthic macrofaunal populations and environmental drivers in the Bering Strait region. Our focus was on the waters of the northern Bering and southern Chukchi Seas, which are shallow (<100 m) and seasonally productive, with strong pelagic-benthic coupling between water column derived organic matter and the seafloor. Studies indicate that both in situ production and advection of upstream phytodetritus support persistent biologically productive regions, termed hotspots, in the greater Bering Strait region. The benthic marine ecosystem is dominated by macroinvertebrates (e.g., clams, polychaetes, and amphipods) that in turn serve as food resources for diving mammals and seabirds, thus allowing for changes to cascade strongly through the food web from prey to predator. During our study, the persistence of seasonal sea ice significantly declined; trend analyses indicate both earlier sea ice breakup and later fall freeze-up in recent years. When combined with warming seawater temperatures in the region, these changes have ramifications for water column processes that influence benthic faunal biomass and composition, which can transfer to upper trophic level predators. We studied these changes by evaluating time series sites in three benthic biomass hotspots starting in 1998 (Southeast Chukchi Sea region), 1999 (Chirikov Basin region), and 2000 (St. Lawrence Island Polynya region). We present these data within a broader evaluation of benthic biomass results from prior cruises dating as early as the 1970s. The current study focuses on the period 1998–2015 at sites occupied annually each July using CCGS Sir Wilfrid Laurier. Since 2010, these time series sites have become part of the international Distributed Biological Observatory (DBO), a network of standard time series stations and transect lines in the Pacific Arctic that is used for evaluating changes within the biological system. We found that these regions have experienced northward shifts in high benthic biomass and changes in dominant macrofaunal composition that are coincident with recent reduced sea ice cover and variable warming of seasonal water column temperatures. Hydrographic changes can influence chlorophyll a inventories in surface sediments and total organic carbon content, both of which are indicators of food supply to the benthos. In addition, sediment grain size reflects variable current flow that in turn influences faunal composition. Time series studies are essential for evaluating whether this region is transitioning or even reaching a “tipping point” that could shift the benthic-dominated system to a pelagic one, with large-scale ramifications for ecosystem structure in this highly productive Pacific Arctic ecosystem. 

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4. Essential omega‐3 fatty acids are depleted in sea ice and pelagic algae of the Central Arctic Ocean

   https://doi.org/10.1111/gcb.17090  

   Schmidt, Katrin; Graeve, Martin; Hoppe, Clara J.; Torres‐Valdes, Sinhué; Welteke, Nahid; Whitmore, Laura M.; Anhaus, Philipp; Atkinson, Angus; Belt, Simon T.; Brenneis, Tina; et al (January 2024, Global Change Biology)

   Abstract Microalgae are the main source of the omega‐3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), essential for the healthy development of most marine and terrestrial fauna including humans. Inverse correlations of algal EPA and DHA proportions (% of total fatty acids) with temperature have led to suggestions of a warming‐induced decline in the global production of these biomolecules and an enhanced importance of high latitude organisms for their provision. The cold Arctic Ocean is a potential hotspot of EPA and DHA production, but consequences of global warming are unknown. Here, we combine a full‐seasonal EPA and DHA dataset from the Central Arctic Ocean (CAO), with results from 13 previous field studies and 32 cultured algal strains to examine five potential climate change effects; ice algae loss, community shifts, increase in light, nutrients, and temperature. The algal EPA and DHA proportions were lower in the ice‐covered CAO than in warmer peripheral shelf seas, which indicates that the paradigm of an inverse correlation of EPA and DHA proportions with temperature may not hold in the Arctic. We found no systematic differences in the summed EPA and DHA proportions of sea ice versus pelagic algae, and in diatoms versus non‐diatoms. Overall, the algal EPA and DHA proportions varied up to four‐fold seasonally and 10‐fold regionally, pointing to strong light and nutrient limitations in the CAO. Where these limitations ease in a warming Arctic, EPA and DHA proportions are likely to increase alongside increasing primary production, with nutritional benefits for a non‐ice‐associated food web. 

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5. Seafloor primary production in a changing Arctic Ocean

   https://doi.org/10.1073/pnas.2303366121  

   Attard, Karl; Singh, Rakesh Kumar; Gattuso, Jean-Pierre; Filbee-Dexter, Karen; Krause-Jensen, Dorte; Kühl, Michael; Sejr, Mikael K.; Archambault, Philippe; Babin, Marcel; Bélanger, Simon; et al (March 2024, Proceedings of the National Academy of Sciences)

   Phytoplankton and sea ice algae are traditionally considered to be the main primary producers in the Arctic Ocean. In this Perspective, we explore the importance of benthic primary producers (BPPs) encompassing microalgae, macroalgae, and seagrasses, which represent a poorly quantified source of Arctic marine primary production. Despite scarce observations, models predict that BPPs are widespread, colonizing ~3 million km²of the extensive Arctic coastal and shelf seas. Using a synthesis of published data and a novel model, we estimate that BPPs currently contribute ~77 Tg C y⁻¹of primary production to the Arctic, equivalent to ~20 to 35% of annual phytoplankton production. Macroalgae contribute ~43 Tg C y⁻¹, seagrasses contribute ~23 Tg C y⁻¹, and microalgae-dominated shelf habitats contribute ~11 to 16 Tg C y⁻¹. Since 2003, the Arctic seafloor area exposed to sunlight has increased by ~47,000 km²y⁻¹, expanding the realm of BPPs in a warming Arctic. Increased macrophyte abundance and productivity is expected along Arctic coastlines with continued ocean warming and sea ice loss. However, microalgal benthic primary production has increased in only a few shelf regions despite substantial sea ice loss over the past 20 y, as higher solar irradiance in the ice-free ocean is counterbalanced by reduced water transparency. This suggests complex impacts of climate change on Arctic light availability and marine primary production. Despite significant knowledge gaps on Arctic BPPs, their widespread presence and obvious contribution to coastal and shelf ecosystem production call for further investigation and for their inclusion in Arctic ecosystem models and carbon budgets. 

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